One-Pot Synthesis for Lithium Ion Battery Cathode Material Precursors

ABSTRACT

Provided is an improved method for forming lithium ion cathode materials specifically for use in a battery. The method comprises forming a first solution comprising a digestible feedstock of a first metal suitable for formation of a cathode oxide precursor and a multi-carboxylic acid. The digestible feedstock is digested to form a first metal salt in solution wherein the first metal salt precipitates as a salt of deprotonated multi-carboxylic acid thereby forming an oxide precursor. The oxide precursor is heated to form the lithium ion cathode material.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to pending U.S. Provisional Patent Application No. 62/447,598 filed Jan. 18, 2017 and pending U.S. Provisional Patent Application No. 62/483,777 filed Apr. 10, 2017 both of which are incorporated herein by reference.

BACKGROUND

The present application is related to an improved method of forming fine and ultrafine powders and nanopowders of lithium ion cathodes for batteries. More specifically, the present invention is related to, but not limited to, lithium ion battery cathodes and an efficient method of preparing the spinel materials and other advanced materials with minimal waste of material and a reduction in the process steps which are detrimental to subsequent steps such as sintering and calcining.

There is an ever present demand for improvements in batteries. There are two primary applications for batteries with one being stationary applications and the other being mobile applications. With both stationary and mobile applications there is a desire for increased storage capacity, longer battery life, the ability to reach full charge quicker and lower cost. Lithium ion batteries, comprising a lithium metal oxide cathode, are highly advantageous as a suitable battery for most applications and they have found favor across the spectrum of applications. Still, there is a desire for an improvement in, particularly, the storage capability, recharge time, cost and storage stability of lithium ion batteries. The present invention is focused, primarily, on lithium ion batteries in a spinel crystalline form or rock-salt crystalline form and improvements in the manufacturing process thereof.

The preparation of lithium ion batteries comprising lithium and transition metal based cathodes in a rock-salt crystalline form are described in U.S. Pat. Nos. 9,136,534; 9,159,999 and 9,478,807 and U.S. Published Pat. Appl. Nos. 2014/0271413; 2014/0272568 and 2014/0272580 each of which are incorporated herein by reference. Cathode materials having a rock-salt crystalline form have general formula:

LiNi_(a)Mn_(b)X_(c)O₂

wherein X is preferably Co or Al and a+b+c=1. When X is cobalt the cathode materials are referred to as NMC's, for convenience, and when X is aluminum the cathode materials are referred to as NCA's, for convenience. In the preparation of the rock-salt crystalline form the transition metals can be precipitated as carbonates by the addition of a stoichiometric equivalent of lithium carbonate to form cathode material precursors. The cathode material precursors are then sintered to form the cathode material

Cathode materials having the spinel crystalline structure have general formula:

LiNi_(x)Mn_(y)Co_(z)O₄

wherein x+y+z=2. In the spinels the lithium stoichiometry is half that of transition metal stoichiometry. Therefore, the carbonate available from lithium carbonate is insufficient to precipitate the transition metals when synthesizing cathode material precursors. The addition of excess carbonate can only be achieved through the introduction of undesirable counterions, such as sodium when sodium carbonate is used, or complicates pH control and may lead to insufficient precipitation, such as when ammonium carbonate is added. A twice stoichiometric excess of lithium carbonate could be used in principle, and removed through decantation of the aqueous supernatant, however this is undesirable due to the sensitivity of cell performance with variation in lithium stoichiometry.

There has been a desire for an improved method of manufacturing lithium ion cathodes and particularly lithium/manganese/nickel based cathodes in a spinel and rock salt crystalline structures. The present invention provides such a method.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an improved method of preparing a cathode for lithium ion batteries.

It is an object of the invention to provide an improved method for forming precursors of a lithium metal oxide which are calcined to form the lithium metal oxide cathode.

It is a particular object of the invention to provide an improved method for forming lithium ion batteries comprising a transition metal based cathode in a spinel crystalline structure or a rock-salt structure preferably chosen from NMC and NCA.

A particular feature of the invention is the ability to manufacture lithium ion metal oxide cathodes comprising a gradient of transition metal composition throughout the oxide predictably and reproducibility thereby allow for alteration of the bulk properties, such as in the core, from the shell properties, such as that portion surrounding the core.

An embodiment of the invention is provided in a method of forming a lithium ion cathode material comprising a digestible feedstock of a metal salt suitable for formation of a cathode oxide precursor and a multi-carboxylic acid; digesting the digestible feedstock to form a metal salt in solution wherein the metal salt precipitates as a salt of deprotonated multi-carboxylic acid thereby forming an oxide precursor; and heating the oxide precursor to form said lithium ion cathode material.

Yet another embodiment is provided in a method of forming a lithium ion cathode material comprising: forming reacting lithium carbonate, manganese carbonate and nickel carbonate with oxalic acid, liberating CO_(2(g)) and/or H₂O_((l)) to forming a precipitate comprising lithium oxalate, manganese oxalate and nickel oxalate to form an oxide precursor; and heating the oxide precursor to form the lithium ion cathode material.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 provides SEM micrographs of oxalate spray dried precursors and LiNi_(0.5)Mn_(1.5)O₄ material calcined at 900° C. for 15 hours when using transition metal acetate (top) and carbonate (bottom) feedstocks.

FIG. 2 provides X-ray Diffraction (XRD) patterns of manganese oxalate hydrates precipitated from the reaction of manganese carbonate and oxalic acid in water in different conditions.

FIG. 3 demonstrates improvements in the specific capacity as a function of voltage for the spinel material formed by the improved process.

FIG. 4 is an XRD pattern of an embodiment of the invention.

FIG. 5 is an SEM micrograph of an embodiment of the invention.

FIG. 6 is an XRD pattern of an embodiment of the invention.

FIG. 7 is SEM micrograph of an embodiment of the invention.

FIG. 8 is a graphical representation of an embodiment of the invention.

FIG. 9 is a graphical representation of an embodiment of the invention.

FIG. 10 is a graphical representation of an embodiment of the invention.

FIG. 11 is a graphical representation of an embodiment of the invention.

FIG. 12 is a graphical representation of an embodiment of the invention.

FIG. 13 is an XRD pattern of an embodiment of the invention.

FIG. 14 is a graphical representation of an embodiment of the invention.

FIG. 15 is a graphical representation of an embodiment of the invention.

FIG. 16 is a graphical representation of an embodiment of the invention.

FIG. 17 is an XRD pattern of an embodiment of the invention.

FIG. 18 is a graphical representation of an embodiment of the invention.

FIG. 19 is a graphical representation of an embodiment of the invention.

FIG. 20 is a graphical representation of an embodiment of the invention.

FIG. 21 is a graphical representation of an embodiment of the invention.

FIG. 22 is a graphical representation of an embodiment of the invention.

FIG. 23 is a graphical representation of an embodiment of the invention.

FIG. 24 is a graphical representation of an embodiment of the invention.

FIG. 25 is an XRD pattern of an embodiment of the invention.

FIG. 26 is an XRD pattern of an embodiment of the invention.

FIG. 27 is an XRD pattern of an embodiment of the invention.

FIG. 28 is an XRD pattern of an embodiment of the invention.

FIG. 29 is a SEM micrograph of an embodiment of the invention.

FIG. 30 is an XRD pattern of an embodiment of the invention.

FIG. 31 is an XRD pattern of an embodiment of the invention.

FIG. 32 is SEM micrograph of an embodiment of the invention.

FIG. 33 is SEM micrograph of an embodiment of the invention.

FIG. 34 is a graphical representation of an embodiment of the invention

FIG. 35 is an XRD pattern of an embodiment of the invention.

FIG. 36 is an XRD pattern of an embodiment of the invention.

FIG. 37 is SEM micrograph of an embodiment of the invention.

FIG. 38 is SEM micrograph of an embodiment of the invention.

FIG. 39 is a graphical representation of an embodiment of the invention.

FIG. 40 is a graphical representation of an embodiment of the invention.

FIG. 41 is an XRD pattern of an embodiment of the invention.

FIG. 42 is a graphical representation of an embodiment of the invention.

FIG. 43 is a graphical representation of an embodiment of the invention.

FIG. 44 is an XRD pattern of an embodiment of the invention.

FIG. 45 is SEM micrograph of an embodiment of the invention.

FIG. 46 is a graphical representation of an embodiment of the invention.

FIG. 47 is an XRD pattern of an embodiment of the invention.

FIG. 48 is SEM micrograph of an embodiment of the invention.

FIG. 49 is an XRD pattern of an embodiment of the invention.

FIG. 50 is SEM micrograph of an embodiment of the invention.

FIG. 51 is a graphical representation of an embodiment of the invention.

FIG. 52 is a graphical representation of an embodiment of the invention.

FIG. 53 is a graphical representation of an embodiment of the invention.

DESCRIPTION

The instant invention is specific to an improved method for preparing a lithium ion battery, and particularly the cathode of a lithium ion battery. More particularly, the present invention is specific to an improved process for forming cathodes for use in a lithium ion battery wherein the cathode is in a spinel crystalline form or a rock-salt form with preferred rock salt forms being NMC and NCA materials.

In a preferred embodiment the lithium metal compound of the instant invention comprises lithium metal compound in a spinel crystal structure defined by the Formula I:

LiNi_(x)Mn_(y)Co_(z)E_(w)O₄   Formula I

wherein E is an optional dopant; and x+y+z+w=2 and w≤0.2; or a rock-salt crystal structure defined by Formula II;

LiNi_(a)Mn_(b)X_(c)G_(d)O₂   Formula II

wherein G is an optional dopant;

X is Co or Al; and

wherein a+b+c+d=1 and d≤0.1.

In a preferred embodiment in the spinel crystal structure of Formula I has 0.5≤≤x≤0.6; 1.4≤y≤1.5 and z≤0.9. More preferably 0.5≤x≤0.55, 1.45≤y≤1.5 and z≤0.05. In a preferred embodiment neither x nor y is zero. In Formula I it is preferable that the Mn/Ni ratio is no more than 3, preferably at least 2.33 to less than 3 and most preferably at least 2.6 to less than 3.

In a preferred embodiment in the rock-salt crystal structure of Formula II is a high nickel NMC wherein 0.5≤a≤0.9 and more preferably 0.58≤a≤0.62 as represented by NMC 622 or 0.78≤a≤0.82 as represented by NMC 811. In a preferred embodiment a=b=c as represented by NMC 111.

In the formulas throughout the specification, the lithium is defined stoichiometrically to balance charge with the understanding that the lithium is mobile between the anode and cathode. Therefore, at any given time the cathode may be relatively lithium rich or relatively lithium depleted. In a lithium depleted cathode the lithium will be below stoichiometric balance and upon charging the lithium may be above stoichiometric balance. Likewise, in formulations listed throughout the specification the metals are represented in charge balance with the understanding that the metal may be slightly rich or slightly depleted, as determined by elemental analysis, due to the inability to formulate a perfectly balanced stoichiometry in practice.

Dopants can be added to enhance the properties of the oxide such as electronic conductivity and stability. The dopant is preferably a substitutional dopant added in concert with the primary nickel, manganese and optional cobalt or aluminum. The dopant preferably represents no more than 10 mole % and preferably no more than 5 mole % of the oxide. Preferred dopants include Al, Gd, Ti, Zr, Mg, Ca, Sr, Ba, Mg, Cr, Cu, Fe, Zn, V, Bi, Nb and B with Al and Gd being particularly preferred.

The cathode is formed from an oxide precursor comprising salts of Li, Ni, Mn, Co, Al or Fe as will be more fully described herein. The oxide precursor is calcined to form the cathode material as a lithium metal oxide. The cathode material is optionally treated with a phosphate salt, XPO₄, wherein X is the atoms necessary to balance the charge and X may be a monovalent atom, a divalent atom or a trivalent with the understanding that combinations may be used as desired. It is particularly preferred that X be easily removed either by washing or vaporization after application. The phosphate salt is applied to the surface of the metal oxide wherein the phosphate moiety forms a MnPO₄ on the surface of the metal oxide, or bonded to the surface of the metal oxide. The manganese is preferably predominantly in the +3 oxidation state with preferably less than 10% of the surface manganese being in the +2 oxidation state and the manganese thereby stabilized against reduction to Mn²⁺ at the surface. The reaction liberates X which is removed by washing or vaporization. In preferred phosphates, X is selected from NH₄ ⁺, H⁺, Li⁺, Na⁺, and combinations thereof. Particularly preferred phosphates include (NH₄)₃PO₄, (NH₄)₂HPO₄, (NH₄)H₂PO₄, and H₃PO₄ due to the ease of removal of X after formation of the surface manganese phosphate. It is preferred that the native manganese oxide of the calcined oxide precursor be reacted with phosphate as opposed to an added manganese or other metal. Therefore, it is preferred that the added phosphate be relatively free of Mn and more preferably less than 1 wt % manganese. It is preferable that no Mn⁺² be added with the phosphate or after formation of the oxide. It is preferable that there be no separate manganese phosphate phase such as manganese phosphate as a distinct phase on the surface. It is preferable that the phosphate ligate the surface of the metal oxide.

The oxide precursors are formed by the reaction of salts in the presence of counterions which form relatively insoluble salts. The relatively insoluble salts are believed to form suspended crystals which are believed to Ostwald ripen ultimately precipitating as an ordered lattice. For the purposes of the present invention salts of preferably manganese and nickel, and optionally cobalt or aluminum, combined in a solution comprising counterions which precipitate the manganese, nickel and cobalt or aluminum at a rate sufficient to allow crystalline growth. Soluble counterions of manganese, nickel, cobalt or aluminum are those having a solubility of at least 0.1 g of salt per 100 gram of solvent at 20° C. including acetate, nitrate, hydrogen carbonate. The metals are precipitated as insoluble salts have a solubility of less than 0.05 g of salt per 100 gram of solvent at 20° C. including carbonates and oxalates.

The overall reaction comprises two secondary reactions, in sequence, with the first reaction being the digestion of carbonate feedstock in the presence of an excess of multi-carboxylic acid as represented by Reaction A:

XCO₃(s)+2H⁺(aq)⇒X²⁺+CO₂(g)+H₂O(l)  A

wherein X represents a metal suitable for use in a cathode material preferably chosen from Li₂, Mn, Ni, Co or Al. In Reaction A the acid is liberated by the multi-carboxylic acid which is not otherwise represented in Reaction A for simplicity. The result of Reaction A is a metal salt in solution wherein the salt is chelated by the deprotonated multi-carboxylic acid as represented by Reaction B:

X²⁺+⁻OOCR₁COO⁻→X(OOCR₁COO)  B

wherein R¹ represents an alkyl chain comprising the multi-carboxylate. The salts represented by X(OOCR₁COO) precipitate in an ordered lattice as discussed elsewhere herein.

The metal carbonates of Reaction A can be substituted with metal acetates such as Li(O₂CCH₃), Ni(O₂CCH₃)₂ or Mn(O₂CCH₃)₂ which can be added as aqueous solutions or as solid materials.

The pH may be adjusted with ammonium hydroxide, if desired, due to the simplicity and improved ability to accurately control the pH. In the prior art processes the use of ammonium hydroxide caused difficulty due to the propensity for NH₃ to complex with nickel in aqueous solution as represented by the reaction:

[Ni(H₂O)₆]²⁺ +xNH₃⇒[Ni(NH₃)_(x)(H₂O)_(6-x)]²⁺ xH₂O

The result is incomplete precipitation of nickel which complicates determination and control of stoichiometry of the final oxide precursor. Multi-carboxylic acids, and particularly oxalic acid, effectively coordinates nickel preferentially over NH₄ ⁺ thereby increasing the rate of precipitation and incorporation of nickel into the ordered oxide precursor. Preferential precipitation by multi-carboxylic acids drives the reaction towards nickel precipitation and avoids the use of ammonium hydroxide.

A particularly preferred embodiment is represented by the formation of LiNi_(0.5)Mn_(1.5)O₄ from the oxide precursor represented by the, preferably aqueous, reaction:

0.5 Li₂CO₃+0.5 NiCO₃+1.5 MnCO₃+2.5 H₂C₂O₄⇒0.5 Li₂C₂O₄+0.5 NiC₂O₄+1.5 MnC₂O₄+2.5 CO₂+2.5 H₂O

wherein the, NiC₂O₄, and MnC₂O₄ precipitate in an ordered lattice as an oxide precursor with Li₂C₂O₄ precipitated thereon upon removal of water. The oxide precursor having the gross composition (Li₂C₂O₄)_(0.5)(NiC₂O₄)_(0.5)(MnC₂O₄)_(1.5) is calcined resulting in the reaction:

(Li₂C₂O₄)_(0.5)(NiC₂O₄)_(0.5)(MnC₂O₄)_(1.5)+2O₂⇒LiNi_(0.5)Mn_(1.5)O₄+5CO₂

The carbonate digestion process in the presence of multi-carboxylic acids includes combining the metal carbonate and oxalic acid into a reactor in the presence of water followed by stirring. The slurry is then dried, preferably by spray drying, followed by calcining. The calcination temperature can vary from 400 to 1000° C. to form materials with different structural properties, for example, different degrees of Mn/Ni cation ordering in spinel LiNi_(0.5)Mn_(1.5)O₄.

A particular feature of the carbonate digestion process is the fact that there is no need to grind or blend the precursor powders, filter the slurry, or decant the supernatant even though these steps can be done if desired.

The carbonate digestion process or digestion(hydrolysis)-precipitation reaction, using oxalate as an example, can be described by the following equation which occurs preferably in the presence of water:

H₂C₂O_(4(aq))+XCO_(3(s))→CO_(2(g))+H₂O_((l))+XC₂O_(4(s,aq)) (X=transition metals,Li₂)

Without being limited to theory, it is hypothesized that the oxalic acid hydrolyses the carbonates to form CO_(2(g)), H₂O_((l)), and metal ions. Transition metal ions are then precipitated as metal oxalates. Lithium oxalate might be precipitated or remain soluble in water, depending on the water content. The soluble lithium oxalate is expected to be coated on transition metal oxalate particles during spray-drying. There is no need to achieve complete dissolution of metal carbonates or oxalic acid as the water is simply a medium to digest the metal carbonates and precipitate out the metal oxalates in a controlled fashion thereby allowing for nucleation and crystal growth. The rate of the digestion(hydrolysis)-precipitation reaction depends on temperature, water content, pH, gas introduction and the crystal structure and morphology of the feedstocks.

The reaction can be completed in the temperature range of 10-100° C. with water reflux temperature being preferred in one embodiment due to the increased digestion reaction rate.

For each 1 g of oxalic acid the water content can vary from about 1 to about 400 ml with a preference for a decreased water content due to the increased reaction rate and less water must be removed subsequently.

The pH of the solution can vary from 0 to 12. A particular advantage of the carbonate digestion process is that the reaction can be done without additional pH control thereby simplifying the process and eliminating the need for additional process control or additions.

Whereas the reaction can be done under untreated atmospheric air other gases such as CO₂, N₂, Ar, other inert gases or O₂ can be used in some embodiments. In some embodiments N₂ and CO₂ bubbling into the solution are preferred as they may slightly increase the crystallinity of the precipitated metal oxalates.

The crystallinity and morphology of the precursors, such as amorphous vs. crystalline carbonate feedstocks can influence the rate of digestion due to the differences in solubility and particle size and range of particle size.

The carbonate digestion process proceeds via a cascading equilibrium from solid carbonate feedstocks to solid oxalate precursor materials. We can separate this process into several distinct processes as per the following reactions for the purposes of discussion without limit thereto:

H₂C₂O_(4(s))→H₂C₂O_(4(aq)) (dissolution of oxalic acid)  (1)

H₂C₂O_(4(aq))←→H⁺ _((aq))+HC₂O₄ ⁻ _((aq)) (oxalic acid dissociation step one, pK_(a)=1.25)  (2)

HC₂O₄ ⁻ _((aq))←→H⁺ _((aq))+C₂O₄ ²⁻ _((aq)) (oxalic acid dissociation step two, pK_(a)=4.19)  (3)

XCO_(3(s,aq))+2H⁺ _((aq))→X²⁺+H₂O_((l))+CO_(2(g)) (carbonate hydrolysis)  (4)

X²⁺ _((aq))+C₂O₄ ²⁻ _((aq))→XC₂O_(4(s)) (precipitation of metal oxalates)  (5)

If this reaction were to be used to create the high voltage LiNi_(0.5)Mn_(1.5)O₄ material, the following reaction would be take place which would be preferably, but not necessarily, in the presence of H₂O:

0.25Li₂CO_(3(s))+0.25NiCO_(3(s))+0.75MnCO_(3(s))+1.25H₂C₂O_(4(aq))→0.25Li₂C₂O_(4(aq))+Ni_(0.25)Mn_(0.75)C₂O_(4(s))+1.25CO_(2(g))+1.25H₂O_((l))  (6)

For the purposes of discussion and explanation the reactions are written stepwise with the understanding that under operational reaction conditions the reactions may be occurring simultaneously. By varying different reaction parameters such as water content/ionic strength, excess oxalic acid content, batch size, temperature, atmosphere, refluxing the reaction mixture, pH control etc. the rates of each step can be controlled and other desirable parameters such as solids content can be optimized.

The carbonate digestion process can be described as proceeding in a cascading equilibrium as the evolution of CO_(2(g)) from solution, as in Reaction 4 above, and precipitation of highly insoluble metal oxalates, as in Reaction 5 above, both drive the reaction to completion.

Rates of carbonate hydrolysis are correlated to K_(sp) of the metal carbonate with the following provided for convenience:

Lithium carbonate, Li₂CO₃, 8.15×10⁻⁴ Very fast (seconds to minutes); Nickel(II) carbonate, NiCO₃, 1.42×10⁻⁷ Fast (minutes); Manganese(II) carbonate, MnCO₃, 2.24×10⁻¹¹ Slower (hours to days); and Aluminum hydroxide (Al(OH)₃, 3×10⁻³⁴ Very slow

The homogeneity of co-precipitation could depend on rates of carbonate hydrolysis. For example, if Nickel(II) carbonate is fully hydrolyzed before Manganese(II) carbonate, it may subsequently precipitate as NiC₂O₄ and MnC₂O₄ separately.

Temperature can be controlled as it influences the rates of dissolution of oxalic acid, carbonate hydrolysis, and precipitation of metal oxalates. Specifically, it would be useful to perform the reaction at water reflux temperature. CO_(2(g)) is produced in this reaction, and raising the temperature will increase the rate of removal of CO_(2(g)), and therefore due to lower aqueous CO_(2(g)) solubility at high temperatures increasing the temperature may increase the rate of carbonate hydrolysis.

Gas bubbling may also be an effective method of controlling the rates of reaction by altering the rate of CO₂ evolution. Bubbling of N_(2(g)), O_(2(g)), CO_(2(g)), and/or atmospheric air may be beneficial as the gases may function to displace dissolve CO_(2(g)) or improve mixing of reactants.

The carbonates may digest faster if they are first in the form of the metastable bicarbonate. For example, the following reaction occurs for Li₂CO₃:

Li₂CO_(3(s))+CO_(2(g))+H₂O_((l))←→2LiHCO_(3(aq))

The metastable lithium bicarbonate is far more soluble than Li₂CO₃ and the subsequent hydrolysis can proceed stoichiometrically with a single proton as shown below:

LiHCO_(3(aq))+H⁺ _((aq))→H₂O_((l))+CO_(2(g))+Li⁺ _((aq)l)

as opposed to proceeding as Reaction 4 above.

Divalent metal oxalates such as NiC₂O₄, MnC₂O₄, CoC₂O₄, ZnC₂O₄, etc. are highly insoluble, however monovalent metal oxalates such as Li₂C₂O₄ are somewhat soluble with a solubility of 8 g/100 mL at 25° C. in water. If it is necessary to have the lithium oxalate in solution and homogeneously dispersed throughout a mixed metal oxalate precipitate, then keeping the water volume above the solubility limit of lithium oxalate may be necessary.

The rates of carbonate hydrolysis, metal oxalate precipitation, and the crystal structure and particle size of the metal oxalate precipitate is influenced by pH and water content or ionic strength. In some embodiments it may be beneficial to work at higher ionic strength, or lower water content as this increases the proton activity of oxalic acid, and rates of precipitation of metal oxalates. Water content can be normalized to carbonate feedstock content with a preferred ratio of moles carbonates to volume of water in L being in the range of about 0.05 to about 20. A water content of about 1.64 L per 1.25 moles of carbonates providing a ratio of moles of carbonates to volume of water in L as 1.79 which is suitable for demonstration of the invention.

A stoichiometric amount of oxalate to carbonate is sufficient to achieve complete precipitation. However, adding excess oxalic acid can increase the reaction rate as the second proton on oxalic acid is much less acidic and is involved in the hydrolysis. About 5% excess oxalic acid by mole to carbonates is sufficient to ensure completion of carbonate hydrolysis. ICP analyses have shown that 10% excess oxalic acid leaves a similar number of Mn/Ni ions in solution as 0% stoichiometric excess by the completion of the reaction. A small stoichiometric excess of oxalic acid should be effective in achieving complete precipitation however a low stoichiometric excess may impact the rate of carbonate hydrolysis.

A particular advantage of the carbonate digestion process is the ability to do the entire reaction in a single reactor until completion. As the lithium source is ideally in solution prior to the spray drying and calcination steps, it may be useful and/or possible to precipitate the transition metals separately and to add the lithium source after co-precipitation as a solution of an aqueous lithium salt such as oxalate.

The invention is suitable for use with transition metal acetates and mixed carbonate feedstocks thereby allowing the solubility of the metal complexes to be more closely matched. Mixed carbonate feedstock such as Ni_(0.25)Mn_(0.75)CO₃+Li₂CO₃ to produce a LiNi_(0.5)Mn_(1.5)O₄ material are contemplated. Feedstock impurities may be critical to the performance of final materials. In particular, samples of MnCO₃ may have small quantities of unknown impurities which are not hydrolyzed during refluxing.

Multi-carboxylic acids comprise at least two carboxyl groups. A particularly preferred multi-carboxylic acid is oxalic acid due, in part, to the minimization of carbon which must be removed during calcining. Other low molecular weight di-carboxylic acids can be used such as malonic acid, succinic acid, glutaric acid and adipic acid. Higher molecular weight di-carboxylic acids can be use, particularly with an even number of carbons which have a higher solubility, however the necessity of removing additional carbons and decreased solubility renders them less desirable. Other acids such as citric, lactic, oxaloacetic, fumaric, maleic and other polycarboxylic acids can be utilized with the proviso they have sufficient solubility to achieve at least a small stoichiometric excess and have sufficient chelating properties. It is preferable that acids with hydroxyl groups not be used due to their increased hygroscopic characteristics.

To accomplish the reaction to form the oxide precursor solutions of the starting salts are prepared. It is preferable to prepare added solutions, preferably comprising the nickel, manganese and cobalt or aluminum solutions either collectively, separately, or in some combination, and a bulk solution preferably comprising the lithium. The added solution is then added, as described elsewhere herein, to the bulk solution. The solutions can be reversed, however, it is preferable that the transition metals be added in the intended stoichiometry and it is therefore advantageous to add as a single solution comprising all transition metals to a lithium containing bulk solution.

Each solution is prepared by dissolving the solid in a selected solvent, preferably a polar solvent, such as water, but not limited thereto. The choice of the solvent is determined by the solubility of the solid reactant in the solvent and the temperature of dissolution. It is preferred to dissolve at ambient temperature and to dissolve at a fast rate so that solubilization is not energy intensive. The dissolution may be carried out at a slightly higher temperature but preferably below 100° C. Other dissolution aids may be addition of an acid or a base.

During mixing it is preferable to bubble gas into the bulk solution. For the purposes of discussion the gas is defined as inert, which has no contribution to the chemical reaction, or the gas is defined as reactive, which either adjust the pH or contributes to the chemical reaction. Preferred gases include air, CO₂, NH₃, SF₆, HF, HCl, N₂, helium, argon, methane, ethane, propane or mixtures thereof. A particularly preferred gas includes ambient air unless the reactant solutions are air-sensitive. Carbon dioxide is particularly preferred if a reducing atmosphere is required and it can also be used as a dissolution agent, as a pH adjusting agent or as a reactant if carbonates are formed. Ammonia may also be introduced as a gas for pH adjustment. Ammonia can form ammonia complexes with transition metals and may assist in dissolving such solids. Mixtures of gases may be employed such as 10% O₂ in argon as an example.

For the formation of the oxide precursor the pH is preferably at least about 1 to no more than about 9.6 without limit thereto. Ammonia, or ammonium hydroxide, is suitable for increasing pH as is any soluble base with LiOH being particularly preferred for adjustment is necessary. Acids, particularly formic acid, are suitable for decreasing pH if necessary. In one embodiment lithium can be added, such as by addition of lithium acetate to achieve adequate solids content, typically about 20 to 30 wt %, prior to drying.

A particular advantage of the instant invention is the ability to form gradients of transition metal concentration throughout the body of the oxide wherein regions, the center for example, can have one ratio of transition metals and that ratio can vary in either continuous fashion or step-wise fashion through the body of the oxide. Considering NMC for the purposes of discussion and clarification without limit thereto, the concentration of Ni, Mn and Co can change radially from the core towards the surface of a particle. In an exemplary embodiment provided for clarity, the Ni content can be in a gradient thereby allowing a relatively low nickel concentration on or near the surface of the oxide particle and relatively high nickel concentration in the core of the oxide particle. The ratio of Li to transition metals would remain constant, based on neutral stoichiometry, throughout the oxide particle. By way of clarifying example, the overall compositions of Ni:Mn:Co may be 6:2:2 and 8:1:1 for NMC 622 and NMC 811, respectively, with the core being relatively rich in one transition metal and the shell being relative poor in the same transition metal. Even more specifically, the core may be rich in one transition metal, nickel for example, with a radially decreasing ratio in that transition metal relative to the others. An NMC 8:1:1 core, for example may have exterior thereto an NMC 6:2:2 shell with an NMC 1:1:1 shell on the exterior as a non-limiting step-wise example. These reactions can be done in step-wise additions, or in a continuous gradient by altering the pump rates of the transition metals. The ratio of transition metals in each addition and the number of additions can be altered to obtain desired gradient distributions.

A particular feature of the instant invention is the ability to incorporate dopants and other materials either preferentially in the interior of the oxide or towards the surface or even at the surface. With prior art techniques dopants, for example, are homogenously dispersed within the oxide. Furthermore, any surface treatment, such as with aluminum, is on a formed oxide as a surface reactant not necessarily as an atom incorporated into the oxide lattice. The present invention allows dopants to be dispersed systematically at the core, as would be the case if the dopant were incorporated into the initial transition metal slurry, in a radial band, as would be the case if the dopant were incorporated into a subsequent transition metal slurry, or in an outer shell, as would be the case if the dopant were incorporated into the final transition metal slurry.

For the purposes of the instant invention, each radial portion of the oxide particle will be defined based on the percentage of transition metal used to form the portion. By way of example, if the initial slurry has a first ratio of transition metals, and the initial slurry comprises 10 mol % of the total transition metal used to form the oxide, the core will be considered to be 10% of the volume of the oxide and the composition of the core will be defined as having the same ratio as the first ration of transition metals. Similarly, each shell surrounding the core will be defined by the percentage of transition metal therein. By way of non-limiting example, a precursor to the oxide formed with three slurries, each of equal moles of transition metal, wherein the first slurry had a Ni:Mn:Co ratio of 8:1:1, the second slurry had a Ni:Mn:Co ratio of 6:2:2 and the third slurry had a Ni:Mn:Co ratio of 1:1:1 would be considered to form an oxide representing ⅓ of the volume of the oxide particle being a core with transition metals in the ratio of 8:1:1, a first shell on the core representing ⅓ of the volume of the oxide particle with a transition metal ratio of 6:2:2 and an outer shell on the first shell representing ⅓ of the volume of the oxide particle with a transition metal ratio of 1:1:1 without regards for the migration of transition metals which may occur during sintering of the precursor to the oxide.

In a particularly preferred embodiment, a dopant is incorporated into an outer shell with a particular dopant being aluminum. More preferably, the outer shell comprising the dopant represents less than 10% of the volume of the oxide particle, even more preferably less than 5% of the volume of the oxide particle and most preferably no more than 1% of the volume of the oxide particle. For the purposes of the present invention a dopant is defined as a material precipitated during the formation of the precursor to the oxide in concert with at least one transition metal selected from Ni, Mn, Co, Al and Fe. More preferably, the precursor to the oxide comprises Ni and Mn and optionally either Co or Al. A material added after completion of the precipitation of at least one transition metal is defined herein as a surface treatment.

Upon completion of the reaction to form the oxide precursor, the resulting slurry mixture is dried to remove the solvent and to obtain the dried precursor powder. Any type of drying method and equipment can be used including spray dryers, tray dryers, freeze dryers and the like, chosen depending on the final product preferred. The drying temperatures would be defined and limited by the equipment utilized and such drying is preferably at less than 350° C. and more preferably 200-325° C. Drying can be done using an evaporator such that the slurry mixture is placed in a tray and the solvent is released as the temperature is increased. Any evaporator in industrial use can be employed. A particularly preferred method of drying is a spray dryer with a fluidized nozzle or a rotary atomizer. These nozzles are preferably the smallest size diameter suitable for the size of the oxide precursor in the slurry mixture. The drying medium is preferably air due to cost considerations.

The particle sizes of the oxide precursor are of nanosize primary and secondary particles and up to small micron size secondary particles ranging to less than 50 micron aggregates which are very easily crushed to smaller size. It should be known that the composition of the final powder influences the morphology as well. The oxide precursor has a preferred particle size of about 1-5 μm. The resulting mixture is continuously agitated as it is pumped into the spray dryer head if spray dryers, freeze dryers or the like are used. For tray dryers, the liquid evaporates from the surface of the solution.

The dried powders are transferred into the calcining system batch-wise or by means of a conveyor belt. In large scale production, this transfer may be continuous or batch. The calcining system may be a box furnace utilizing ceramic trays or saggers as containers, a rotary calciner, a fluidized bed, which may be co-current or counter-current, a rotary tube furnace and other similar equipment without limit thereto.

The heating rate and cooling rate during calcinations depend on the type of final product desired. Generally, a heating rate of about 5° C. per minute is preferred but the usual industrial heating rates are also applicable.

The final powder obtained after the calcining step is a fine, ultrafine or nanosize powder that may not require additional crushing, grinding or milling as is currently done in conventional processing. Particles are relatively soft and not sintered as in conventional processing.

The final calcined oxide powder is preferably characterized for surface area, particle size by electron microscopy, porosity, chemical analyses of the elements and also the performance tests required by the preferred specialized application.

The spray dried oxide precursor is preferably very fine and nanosize.

A modification of the spray dryer collector such that an outlet valve opens and closes as the spray powder is transferred to the calciner can be implemented. Batchwise, the spray dried powder in the collector can be transferred into trays or saggers and moved into a calciner. A rotary calciner or fluidized bed calciner can be used to demonstrate the invention. The calcination temperature is determined by the composition of the powder and the final phase purity desired. For most oxide type powders, the calcination temperatures range from as low as 400° C. to slightly higher than 1000° C. After calcination, the powders are sieved as these are soft and not sintered. The calcined oxide does not require long milling times nor classifying to obtain narrow particle size distribution.

The LiM₂O₄ spinel oxide has a preferred crystallite size of 1-5 μm. The LiMO₂ rock salt oxide has a preferred crystallite size of about 50-250 nm and more preferably about 150-200 nm.

A particular advantage of the present invention is the formation of metal chelates of multi-carboxylic acids as opposed to acetates. Acetates function as a combustion fuel during subsequent calcining of the oxide precursor and additional oxygen is required for adequate combustion. Lower molecular weight multi-carboxylic acids, particularly lower molecular weight dicarboxylic acids, and more particularly oxalic acid, decompose at lower temperatures without the introduction of additional oxygen. The oxalates, for example, decompose at about 300° C., without additional oxygen, thereby allowing for more accurate control of the calcining temperature. This may allow for reduced firing temperatures thereby facilitating the formation of disordered Fd3m spinel crystalline structures with minimal impurity phase occurring as seen at high temperature

This method for forming the oxide precursor is referred to herein as the complexometric precursor formulation (CPF) method which is suitable for large scale industrial production of high performance fine, ultrafine and nanosize powders requiring defined unique chemical and physical properties that are essential to meet performance specifications for specialized applications. The CPF method provides an oxide precursor wherein the metals are precipitated as salts into an ordered lattice. The oxide precursor is then calcined to form the oxide. While not limited to theory, it is hypothesized that the formation of an ordered lattice, as opposed to an amorphous solid, facilitates oxide formation during calcination.

The CPF method provides for the controlled formation of specialized microstructures or nanostructures and a final product with particle size, surface area, porosity, phase purity, chemical purity and other essential characteristics tailored to satisfy performance specifications. Powders produced by the CPF method are obtained with a reduced number of processing steps relative to currently used technology and can utilize presently available industrial equipment.

The CPF method is applicable to any inorganic powder and organometallic powders with electrophilic or nucleophilic ligands. The CPF method can use low cost raw materials as the starting raw materials and if needed, additional purification or separation can be done in-situ. Inert or oxidative atmospheric conditions required for powder synthesis are easily achieved with the equipment for this method. Temperatures for the reactions can be ambient or slightly warm but preferably not more than 100° C.

The CPF method produces fine, ultrafine and nanosize powders of precursor oxides in a simple efficient way by integrating chemical principles of crystallization, solubility, transition complex formation, phase chemistry, acidity and basicity, aqueous chemistry, thermodynamics and surface chemistry.

The time when crystallization begins and, in particular, when the nucleation step begins, is the most crucial stage of formation of nanosize powders. A particular advantage provided by CPF is the ability to prepare the nanosize particles at the onset of this nucleation step. The solute molecules from the starting reactants are dispersed in a given solvent and are in solution. At this instance, clusters are believed to begin forming on the nanometer scale under the right conditions of temperature, supersaturation, and other conditions. These clusters constitute the nuclei wherein the atoms begin to arrange themselves in a defined and periodic manner which later defines the crystal microstructure. Crystal size and shape are macroscopic properties of the crystal resulting from the internal crystal lattice structure.

After the nucleation begins, crystal growth also starts and both nucleation and crystal growth may occur simultaneously as long as supersaturation exists. The rate of nucleation and growth is determined by the existing supersaturation in the solution and either nucleation or growth occurs over the other depending on the supersaturation state. It is critical to define the concentrations of the reactants required accordingly in order to tailor the crystal size and shape. If nucleation dominates over growth, finer crystal size will be obtained. The nucleation step is a very critical step and the conditions of the reactions at this initial step define the crystal obtained. By definition, nucleation is an initial phase change in a small area such as crystal forming from a liquid solution. It is a consequence of rapid local fluctuations on a molecular scale in a homogeneous phase that is in a state of metastable equilibrium. Total nucleation is the sum effect of two categories of nucleation—primary and secondary. In primary nucleation, crystals are formed where no crystals are present as initiators. Secondary nucleation occurs when crystals are present to start the nucleation process. It is this consideration of the significance of the initial nucleation step that forms the basis for the CPF method.

In the CPF method, the reactants are dissolved in a solution preferably at ambient temperature or if needed, at a slightly elevated temperature but preferably not more than 100° C. Selection of inexpensive raw materials and the proper solvent are important aspects of this invention. The purity of the starting materials are also important since this will affect the purity of the final product which may need specified purity levels required for its performance specifications. As such, low cost starting materials which can be purified during the preparation process without significantly increasing the cost of processing must be taken into consideration.

CPF uses conventional equipment to intimately mix reactants and preferably includes a highly agitated mixture preferably with bubbling of gas, particularly, when reactant gas is advantageous.

It is preferred that the gas be introduced directly into the solution without limit to the method of introduction. The gas can be introduced into the solution within the reactor by having several gas diffusers, such as tubes, located on the side of the reactor, wherein the tubes have holes for the exit of the gas. Another configuration is to have a double wall reactor such that the gas passes through the interior wall of the reactor. The bottom of the reactor can also have entry ports for the gas. The gas can also be introduced through the agitator shaft, creating the bubbles upon exiting. Several other configurations are possible and the descriptions of these arrangements given herein are not limited to these.

In one embodiment an aerator can be used as a gas diffuser. Gas diffusing aerators can be incorporated into the reactor. Ceramic diffusing aerators which are either tube or dome-shaped are particularly suitable for demonstration of the invention. The pore structures of ceramic bubble diffusers can produce relatively fine small bubbles resulting in an extremely high gas to liquid interface per cubic feet per minute (cfm) of gas supplied. A ratio of high gas to liquid interface coupled with an increase in contact time due to the slower rate of the fine bubbles can provide for a higher transfer rates. The porosity of the ceramic is a key factor in the formation of the bubble and significantly contributes to the nucleation process. While not limited thereto for most configurations a gas flow rate of at least one liter of gas per liter of solution per minute is suitable for demonstration of the invention.

A ceramic tube gas diffuser on the sides of the reactor wall is particularly suitable for demonstration of the invention. Several of these tubes may be placed in different positions, preferably equidistant from each other, to more uniformly distribute gas throughout the reactor. The gas is preferably introduced into the diffuser within the reactor through a fitting connected to the header assembly which slightly pressurizes the chamber of the tube. As the gas permeates through the ceramic diffuser body, fine bubbles may start to form by the porous structure of the material and the surface tension of the liquid on the exterior of the ceramic tube. Once the surface tension is overcome, a minute bubble is formed. This small bubble then rises through the liquid forming an interface for transfer between gas and liquid before reaching the surface of the liquid level.

A dome-shaped diffuser can be placed at the bottom of the reactor or on the sides of the reactor. With dome shaped diffusers a plume of gas bubbles is typically created which is constantly rising to the surface from the bottom providing a large reactive surface.

A membrane diffuser which closes when gas flow is not enough to overcome the surface tension is suitable for demonstration of the invention. This is useful to prevent any product powder from being lost into the diffuser.

In order to have higher gas efficiencies and utilization, it is preferred to reduce the gas flow and pressure and expend less pumping energy. A diffuser can be configured such that for the same volume of gas, smaller bubbles are formed with higher surface area than if fewer larger bubbles are formed. The larger surface area means that the gas dissolves faster in the liquid. This is advantageous in solutions wherein the gas is also used to solubilize the reactant by increasing its solubility in the solution.

Nozzles, preferably one way nozzles, can be used to introduce gas into the solution reactor. The gas can be delivered using a pump and the flow rate should be controlled such that the desired bubbles and bubble rates are achieved. A jet nozzle diffuser, preferably on at least one of the sides or bottom of the reactor, is suitable for demonstration of the invention.

The rate of gas introduction is preferably sufficient to increase the volume of the solution by at least 5% excluding the action of the agitator. In most circumstances at least about one liter of gas per liter of solution per minute is sufficient to demonstrate the invention. It is preferable to recycle the gas back into the reactor.

Transfer of the added solution into the bulk solution is preferably done using a tube attached to a pump connecting the solution to be transferred to the reactor. The tube into the reactor is preferably a tube with a single orifice or several orifices of a chosen predetermined internal diameter such that the diameter size can deliver a stream of the added solution at a given rate. Atomizers with fine nozzles are suitable for delivering the added solution into the reactor. The tip of this transfer tube can comprise a showerhead thereby providing several streams of the added solution simultaneously. In large scale production, the rate of transfer is a time factor so the transfer rate should be sufficiently rapid enough to produce the right size desired.

The agitator can be equipped with several propellers of different configurations, each set comprising one or more propellers placed at an angle to each other or on the same plane. Furthermore, the mixer may have one or more sets of these propellers. The objective is to create sufficient turbulence for adequate solution turnover. Straight paddles or angled paddles are suitable. The dimensions and designs of these paddles determine the type of flow of the solution and the direction of the flow. A speed of at least about 100 rotations per minute (rpm's) is suitable for demonstration of the invention.

The rate of transfer of added solution to the bulk solution has a kinetic effect on the rate of nucleation. A preferred method is to have a fine transfer stream to control the local concentration of the reactants which influences nucleation and the rate of nucleation over the rate of crystal growth. For smaller size powder, a slower transfer rate will yield finer powders. The right conditions of the competing nucleation and growth must be determined by the final powder characteristics desired. The temperature of reaction is preferably ambient or under mild temperatures if needed.

Special nanostructures are preformed which are carried over to the final product thus enhancing the performance of the material in the desired application. For the purposes of the present invention nanostructures are defined as structures having an average size of 100 to 300 nm primary particles.

Neither surfactants nor emulsifiers are necessary. In fact, it is preferable that surfactants and emulsifiers are not used since they may inhibit drying.

Size control can be done by concentration of the solutions, flow rate of the gas or transfer rate of added solution to the bulk solution.

No repetitive and cumbersome milling and classification steps are used.

Reduced calcination time can be achieved and repetitive calcinations are typically not required.

Reaction temperature is ambient. If need for solubilization, temperature is increased but preferably not more than 100° C.

Tailored physical properties of the powder such as surface area, porosity, tap density, and particle size can be carefully controlled by selecting the reaction conditions and the starting materials.

The process is easily scalable for large scale manufacturing using presently available equipment and/or innovations of the present industrial equipment.

EXAMPLES Electrode Preparations:

The composite electrodes were prepared by mixing the active material with 10 wt % conductive carbon black, as a conductive additive, 5 wt % polyvinylidene fluoride (PVDF), as a binder, dissolved in N-methyl-2-pyrrolidinone (NMP) solvent. The slurry was cast on graphite-coated aluminum foil and dried overnight at 60° C. under vacuum. Electrode disks with an area of 1.54 cm² were cut form the electrode sheets with a typical loading of 4 mg·cm⁻².

Coin Cell Assembly:

Coin cells were assembled in an argon-filled glovebox. Lithium foil (340 μm) was used as counter and reference electrodes in half-cells, and commercial Li₄Ti₅O₁₂ (LTO) composite electrodes were used as counter and reference electrodes in full-cells. 1 M LiPF₆ in 7:3 (vol %) ethylene carbonate (EC):diethylene carbonate (DEC) was used as the electrolyte. The electrodes were separated by one or two 25 μm thick sheets of Celgard® membranes in half-cells, and one sheet of Celgard membrane full-cells.

Cycling Protocol:

The spinel cathode cells were galvanostatically cycled in the voltage range of 3.5 V-4.9 Vat various C-rates (1C rate equivalent to 146 mAg⁻¹) at 25° C., using an Arbin Instrument battery tester (model number BT 2000). A constant voltage charging step at 4.9 V for 10 minutes was applied to the cells at the end of 1C or higher rate galvanostatic charging steps. The rock-salt NMC cells were galvanostatically cycled in the voltage range of 2.7 V-4.35 V at various C-rates (1C rate equivalent to 200 mAg⁻¹) at 25° C. A constant voltage charging step at 4.35 V for 10 minutes was applied to the cells at the end of 1C or higher rate galvanostatic charging step.

Example 1

An SEM analysis of spray dried mixed oxalate precursor and calcined material from the production of LiNi_(0.5)Mn_(1.5)O₄ cathode material are both crystalline and the use of transition metal acetate and carbonate feedstocks provide a similar material morphology as illustrated in FIG. 1.

Example 2

FIG. 2 shows the XRD patterns of manganese oxalate hydrates precipitated from the reaction of manganese carbonate and oxalic acid (5% excess by mole) in water for 6 hours (a) at room temperature in air (b) at room temperature with nitrogen bubbling (c) at room temperature with carbon dioxide bubbling (d) at water reflux temperature in air and (e) at room temperature in air with water content of 10 times of those in experiments (a-d). The XRD patterns of the materials precipitated in experiments (a-c) matches with that of manganese oxalate dihydrate with space group C2/c. N₂ and CO₂ gas bubbling have slightly affected the crystallinity of the material. The reaction at water reflux temperature (b) has produced two different manganese oxalate dihydrate phases; one in C2/c space group and one in P2₁2₁2₁ space group. A decrease in concentration of the reactants to 1/10th of that in experiments (a-d) resulted in formations of catena-Poly[[[diaquamanganese(II)]-μ-oxalato]monohydrate], which has a one-dimensional chain structure with space group Pcca. These experiments demonstrate the significant effect of reaction conditions, such as temperature, concentration, and atmosphere, on the precipitated product of the reaction of manganese carbonate and oxalic acid in water.

Example 3

A particular problem with LiNi_(0.5)MN_(1.5)O₄ spinels is the phenomenon referred to as the 4V plateau wherein the voltage drops from 4.7 V to 4.0 V at the end of discharge as illustrated in FIG. 3. The plateau is believed to be the result of Mn³⁺ being formed due to oxygen loss during firing in air. In the results with the prior art process illustrated in FIG. 3 an ordered precursor to the oxide was formed as a precipitate comprising nickel carbonate and manganese carbonate, with stoichiometric lithium acetate, the precursor to the oxide was calcined providing a spinel of LiNi_(0.43)Mn_(1.57)O₄ wherein the Mn:Ni ratio was 3.70. The charge capacity as a function of voltage was measured resulting in the significant 4 volt plateau illustrated in FIG. 3.

In Inventive A the oxalate salts were formed from transition metal acetates resulting in a significant reduction in the 4-volt plateau as illustrated in FIG. 3. In Inventive A, an ordered precursor to the oxide was formed from lithium carbonate, nickel acetate and manganese acetate with oxalic acid digestion in a process referred to in FIG. 3. The precursor to the oxide was then calcined providing a spinel of LiNi_(0.48)Mn_(1.52)O₄ wherein the Mn:Ni ratio was 3.13. The discharge capacity as a function of voltage was measured resulting in a significant reduction of the 4 volt plateau as illustrated in FIG. 3.

In Inventive B metal carbonates are used as the feedstock, with oxalate digestion of the carbonates resulting in the 4-volt plateau being essentially eliminated particularly with the use of a slight excess of nickel wherein the ratio of Mn to Ni is no more than 3, preferably at least 2.33 to less than 3 and most preferably 2.64 to less than 3. An ordered precursor to the oxide was formed from lithium carbonate, nickel carbonate and manganese carbonate with oxalic acid digestion in a process referred to in FIG. 3 as the optimized process. The precursor to the oxide was calcined providing a spinel of LiNi_(0.51)Mn_(1.49)O₄ wherein the Mn:Ni ratio was 2.90. The discharge capacity as a function of voltage was measured resulting in almost complete elimination of the 4 volt plateau as illustrated in FIG. 3.

Example 4

A precursor for a high voltage spinel having a formula of LiNi_(0.5)Mn_(1.5)O₄ was synthesized using lithium carbonate, nickel carbonate, manganese carbonate, and oxalic acid. 820.0 g of H₂C₂O₄.2H₂O was added to 2.0 L of water in a chemical reactor vessel at temperature of about 40° C. In a second vessel a carbonate mixture slurry was prepared comprising Li₂CO₃ (96.1 g), NiCO₃ (148.4 g), MnCO₃ (431.1 g) in 1.2 L of deionized water. The carbonate mixture slurry was pumped into the chemical reactor vessel at a rate of about 0.2-0.3 L/h. The mixture within the reactor was vigorously mixed at 40° C. in ambient atmosphere to form a slurry. The slurry was dried using a spray drier, producing the high voltage spinel precursor material. The X-ray diffraction (XRD) pattern is provided in FIG. 4 and a scanning electron microscopy (SEM) image of the dried powder is provided in FIG. 5. The XRD diffraction indicates a highly ordered crystalline lattice and the SEM demonstrates nanostructured crystalline material.

Example 5

A high voltage spinel having a formula LiNi_(0.5)Mn_(1.5)O₄ was prepared from the precursor of Example 4. The precursor of Example 4 was placed in alumina crucibles and fired in a box furnace in air at 900° C. for 15 h in ambient atmosphere. The resulting powder was analyzed by powder X-ray diffraction analysis resulting in the diffraction pattern provided in FIG. 6. The SEM provided in FIG. 7 illustrates that the nanostructure of the precursor was largely maintained. The lattice parameter of the spinel structure was calculated to be 8.174(1) Å. The electrochemical performance of the synthesized material was evaluated as the cathode in half cells versus lithium metal anodes and in full cells versus Li₄Ti₅O₁₂ (LTO) anodes. The voltage as a function of discharge capacity in a half cell at 0.1C is illustrated in FIG. 8. The specific capacity as a function of cycles at a 1C rate at 25° C. in a half cell is illustrated in FIG. 9. The specific capacity at various discharge rates at 25° C. in a half cell is illustrated in FIG. 10. The specific capacity at at 1C at 25° C. in a full cell with a LTO anode is illustrated in FIG. 11.

Example 6

A high voltage spinel having a formula LiNi_(0.5)Mn_(1.5)O₄ was prepared from the precursor of Example 4. The precursor material was placed in alumina boats and fired in a tube furnace under an oxygen flow of 50 cm³/min. The firing procedure, illustrated in FIG. 12, included a pre-firing step at 350° C., firing at 900° C. and slow cooling to and annealing at 650° C. Firing in oxygen in addition to slow cooling mitigate the oxygen deficiency and leads to a reduction in the 4V plateau commonly observed in these materials. The X-ray diffraction of the obtained powder is provided in FIG. 13 and, based thereon, the lattice parameter of the Spinel structure was calculated to be 8.168(1) Å. The electrochemical performance of the synthesized material was evaluated as the cathode in half cells versus lithium metal anodes. The voltage profile obtained at a discharge rate of 0.1C at 25° C. in a half cell is illustrated in FIG. 14. A particular feature is the absence of a 4V voltage plateau commonly observed in these materials. The specific capacity obtained at a 1C cycle rate at 25° C. in a half cell is illustrated in FIG. 15. The specific capacity of obtained at various discharge rates at 25° C. in a half cell is illustrated in FIG. 16.

Example 7

The precursor material of Example 4 was placed in alumina crucibles and fired in a box furnace in ambient atmosphere using the firing procedure illustrated in FIG. 12. The X-ray diffraction pattern of the resulting powder is provided in FIG. 17 and the lattice parameter of the spinel structure was calculated 8.169(1) Å. The electrochemical performance of the synthesized material was evaluated as the cathode in half cells versus lithium metal anodes. The voltage as a function of discharge capacity at a discharge rate of 0.1C at 25° C. in a half cell is illustrated in FIG. 18. The specific capacity obtained at a 1C discharge rate at 25° C. in a half cell is illustrated in FIG. 19.

Example 8

A precursor to a high voltage spinel having formula LiNi_(0.5)Mn_(1.5)O₄ was synthesized using 8.62 g of MnCO₃ (Alfa; Particle Size: 1-3 μm), 2.97 g of NiCO₃ (Alfa; Anhydrous), and 1.92 g of lithium carbonate as the starting materials. 16.4 g of oxalic acid dihydrate (H₂C₂O₄.2H₂O) was used as the chelating agent. The metal carbonates were mixed with 20 mL of DI water to form a slurry in one beaker and the acid was added to 40 mL of DI water inside a separate beaker. The oxalic acid slurry was then heated to 40° C. and the carbonate slurry was added to the acid solution at a rate of 8.9 mL/hr to form the precursor. The precursor was dried using a spray drier. The dried precursor was fired in an alumina crucible at 900° C. for 15 hours in ambient atmosphere. The voltage as a function of discharge measured at a discharge rate of 0.1C at 25° C. in a half cell is illustrated in FIG. 20.

Example 9

A precursor to a high voltage spinel with formula LiNi_(0.5)Mn_(1.5)O₄ was synthesized similarly to Example 8 except a MnCO₃ with a larger particle size was utilized (Sigma; Particle Size: ≤74 μm). The precursor was dried and fired similarly to Example 8. The voltage as a function of discharge measured at a discharge rate of 0.1C at 25° C. in a half cell is illustrated in FIG. 21.

Example 10

A precursor to a high voltage Spinel LiNi_(0.5)Mn_(1.5)O₄ was synthesized using 8.62 g of MnCO₃ (Sigma; Particle Size: ≤7 m), 2.97 g of NiCO₃ (Alfa; Anhydrous), and 1.92 g of lithium carbonate as the starting materials. 16.4 g of oxalic acid dihydrate (H₂C₂O₄.2H₂O) was used as the chelating agent. The metal carbonates were mixed with 80 mL of DI water to form a slurry in one beaker and the acid was dissolved in 120 mL of DI water inside a separate beaker. The carbonate slurry was added to the oxalic acid solution at ambient temperature of about 25° C. at a rate of 16 mL/hr to form the precursor. The precursor was then dried using a spray drier. The dried precursor was fired in an alumina crucible at 900° C. for 15 hours in ambient atmosphere. The voltage as a function of discharge measured at a discharge rate of 0.1C at 25° C. in a half cell is illustrated in FIG. 22.

Example 11

A precursor to a high voltage Spinel having formula LiNi_(0.5)Mn_(1.5)O₄ was synthesized similarly to Example 10 except less water was used in the reaction: the same amounts of metal carbonates were mixed with 12 mL of DI water and the same amount of oxalic acid was added to 28 mL of water. The carbonate slurry was added to the oxalic acid slurry at the rate of 3 mL/hr. The precursor was then dried and fired similarly to Example 7. The voltage as a function of discharge measured at a discharge rate of 0.1C at 25° C. in a half cell is illustrated in FIG. 23. Example 11 demonstrates the ability to form the precursor with very low amounts of added water, and in some embodiments no water is added, since water is provided by digestion and the waters of hydration of the starting materials may be sufficient to initiate and complete the reaction.

Example 12

A precursor to a high voltage spinel having formula LiNi_(0.5)Mn_(1.5)O₄ was synthesized similarly to Example 11 except a basic nickel carbonate (Sigma; NiCO₃.2Ni(OH)₂.xH₂O), source was used. The precursor was then dried and fired similarly to Example 11. The voltage as a function of discharge measured at a discharge rate of 0.1C at 25° C. in a half cell is illustrated in FIG. 24.

Example 13

A precursor to a high voltage spinel with formula LiNi_(0.5)Mn_(1.5)O₄ was synthesized using 8.62 g of MnCO₃ (Sigma; Particle Size: ≤74 μm), 2.97 g of NiCO₃ (Alfa; Anhydrous), and 1.92 g of lithium carbonate as the starting materials. 16.4 g of oxalic acid dihydrate (H₂C₂O₄.2H₂O) was used as the chelating agent. The metal carbonates were mixed with 80 mL of DI water to form a slurry in one beaker and the acid was dissolved in 160 mL of DI water inside a separate beaker. The beaker with the dissolved oxalic acid was then placed inside an ice bath to maintain a temperature of about 5° C. The carbonate slurry was added to the oxalic acid solution at a rate of 23 mL/hr. An XRD pattern of the dried precursor is provided in FIG. 25.

Example 14

A precursor to a high voltage spinel having formula LiNi_(0.5)Mn_(1.5)O₄ precursor was synthesized similarly to Example 13 except the synthesis was carried out at the boiling point of water (100° C.). A reflux condenser was used to maintain the water level of the reaction. An XRD pattern of the dried precursor is provided in FIG. 26.

Example 15

A precursor to a spinel having formula LiMn₂O₄ was synthesized using lithium carbonate, manganese carbonate, and oxalic acid as starting materials. 16.39 g of H₂C₂O₄.2H₂O was added to 40 ml of water in a beaker. In a second beaker, Li₂CO₃ (1.85 g) and MnCO₃ (11.49 g) were mixed in 24 ml of deionized water. The carbonate mixture slurry was pumped into the oxalic acid slurry with a rate of 0.01 L/Hr. The mixture within the reactor was mixed at ambient temperature. The resulting slurry was dried by evaporating, producing the precursor to the LiMn₂O₄. The XRD pattern is provided in FIG. 27.

The precursor material was fired in a box furnace in air at 350° C. for 1 h and then 850° C. for 5 h. The X-ray diffraction pattern and scanning electron microscopy image of the fired material are shown in FIGS. 28 and 29, respectively.

Example 16

A precursor to a spinel of formula LiMn₂M_(0.1)O₄ (M: Mn, Al, Ni) was synthesized using metal carbonates and oxalic acid, in the amounts shown in Table 1.

The starting materials of each composition was mixed in 32 ml of deionized water for 6 h at ambient temperature. The resulting slurries were dried by evaporation. The X-ray diffraction patterns shown in FIG. 30 show that manganese oxalate dihydrate (Sample A), a precursor to LiMn₂O₄, and the precursor to LiMn_(1.9)Al_(0.1)O₄ (Sample B) crystalized in an orthorhombic space group (P2₁2₁2₁). The to LiMn_(1.9)Ni_(0.1)O₄ (Sample C) crystallized in a monoclinic space group (C2/c).

TABLE 1 Sample Li₂CO₃ MnCO₃ Al(OH)₃ NiCO₃ H₂C₂O₄•2H₂O A 0.961 g 5.745 g 0 0 8.195 g B 0.961 g 5.465 g 0.195 g 0 8.195 g C 0.961 g 5.465 g 0 0.297 g 8.195 g

Example 17

A precursor to NMC 111 having formula LiNi_(0.333)Mn_(0.333)Co_(0.333)O₂ was prepared from 3.88 g Li₂CO₃, 3.79 g NiCO₃, 3.92 g MnCO₃, 3.93 g CoCO₃ and 19.23 g of H₂C₂O₄.2H₂O dispersed in 240 mL of deionized water in a round-bottom flask. The mixture is heated under reflux for 6.5 hour and allowed to cool down. The final mixture had a solids content of approximately 13%. The powder was obtained by spray drying to obtain the precursor with the formula LiNi_(0.333)Mn_(0.333)Co_(0.333)(C₂O₄)_(1.5). The precursor was heated at 110° C. for 1 h and calcined at 800° C. for 7.5 h under air in a box furnace to obtain NMC 111. An SEM of the precursor is provided in FIG. 32. The XRD pattern of the calcined powder is provided in FIG. 31 and the SEM of the calcined powder is provided in FIG. 33 wherein the nanostructure of the precursor is shown to be largely maintained. The discharge capacity as a function of cycles is illustrated in FIG. 34.

Example 18

A precursor to NMC 622 having formula LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ was prepared from 39 g Li₂CO₃, 71 g NiCO₃, 23 g MnCO₃, and 24 g CoCO₃ dispersed in 200 mL of deionized water in a beaker. The mixture of carbonates was pumped into a separate beaker containing 201 g of H₂C₂O₄.2H₂O in 400 mL of deionized water, at a rate of 0.38 moles of carbonates per hour. The reaction mixture is then stirred for 1 h. The final mixture, having a solids content of approximately 20%, was spray dried to obtain the precursor with the formula LiNi_(0.6)Mn_(0.2)Co_(0.2)(C₂O₄)_(1.5). An XRD pattern of the precursor is provided in FIG. 35 and the SEM is provided in FIG. 37. The precursor was heated at 110° C. for 1 h and calcined at 800° C. for 7.5 h under air in a box furnace to obtain NMC 622 with an XRD pattern illustrated in FIG. 36 and an SEM of FIG. 38. The SEM demonstrates that the ordered nanostructure lattice of the precursor is substantially maintained in the calcined powder. The discharge capacity of a half cell at 25° C. at 1C as a function of cycle number is shown in FIG. 39. FIG. 40 shows the initial charge and discharge voltage profiles as a function of capacity at 0.1C.

Example 19

A precursor for NMC 811 having formula LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ was prepared from 39 g Li₂CO₃, 95 g NiCO₃, 12 g MnCO₃, and 12 g CoCO₃ dispersed in 200 mL of deionized water in a beaker. The mixture is pumped into a separate beaker containing 201 g of H₂C₂O₄.2H₂O in 400 mL of deionized water at a rate of 0.38 moles of carbonates per hour. The reaction mixture is then stirred for 1 h. The final mixture having a solids content of approximately 20% was spray dried to obtain the precursor with the formula LiNi_(0.8)Mn_(0.1)Co_(0.1)(C₂O₄)_(1.5). The precursor was heated at 600° C. for 5 h under air in a box furnace, heated at 125° C. for 1 h under oxygen flow, and calcined at 830° C. for 15 h under oxygen flow in a tube furnace to obtain NMC 811. The XRD pattern of the NMC 811 oxide is provided in FIG. 41. The discharge capacity as a function of cycles is provided in FIG. 42 and the voltage profile as function of capacity is illustrated in FIG. 43. The NMC 811 was heated at 125° C. for 1 h and calcined at 830° C. for 15 h under oxygen flow in a tube furnace to form refired NMC 811. The XRD pattern of the refired XRD is provided in FIG. 44 and the SEM is provided in FIG. 45. The discharge capacity is provided in FIG. 46 wherein the solid curve represents the average capacity and the error bars represent the maximum and minimum capacities for a series of samples.

Example 20

A precursor for NCA with formula LiNi_(0.8)Mn_(0.15)Al_(0.05)O₂ was prepared from 8 g Li₂CO₃, 19 g NiCO₃, 2 g Al(OH)(CH₃COO)₂ and 4 g CoCO₃ dispersed in 40 mL of deionized water in a beaker. The mixture was pumped into a separate beaker containing 40 g of H₂C₂O₄.2H₂O in 80 mL of deionized water at a rate of 0.08 moles of carbonates per hour. The reaction mixture was then stirred for 1 h. The final mixture having a solids content of approximately 20% was spray dried to obtain the precursor with the formula LiNi_(0.8)Mn_(0.15)Al_(0.0.05)(C₂O₄)_(1.5). The precursor was heated at 125° C. for 1 h and then calcined at 830° C. for 15 h under oxygen flow in a tube furnace to obtain NCA. The XRD pattern is provided in FIG. 47 and an SEM is provided in FIG. 48 wherein the layered nanostructure originating in the precursor is readily observable.

Example 21

NMC 622 having overall formula LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ was prepared with a step-wise concentration gradient of transition metals from the central portion, or core, to the exterior. The precursor was prepared from 3.9 g Li₂CO₃, 9.5 g NiCO₃, 1.2 g MnCO₃, and 1.2 g CoCO₃ dispersed in 10 mL of deionized water in a beaker. The mixture is pumped into a separate beaker containing 40.4 g of H₂C₂O₄.2H₂O in 80 mL of deionized water to form the core precursor. Subsequently, a mixture comprising 1.0 g Li₂CO₃, 1.8 g NiCO₃, 0.6 g MnCO₃, and 0.6 g CoCO₃ dispersed in 5 mL of deionized water was pumped into the reaction mixture to form a first shell of precursor around the core. An additional mixture comprising 2.9 g Li₂CO₃, 3.0 g NiCO₃, 2.9 g MnCO₃, and 3.0 g CoCO₃ was dispersed in 10 mL of deionized water and pumped into the reaction mixture to form a third ratio in a second shell around the first shell. The addition rates were kept constant at 15 mL per hour for each solution. The reaction mixture was then stirred for 1 h and spray dried to obtain the precursor with the overall formula LiNi_(0.6)Mn_(0.2)Co_(0.2)(C₂O₄)_(1.5). The precursor was then heated at 110° C. for 1 h and calcined at 800° C. for 7.5 h under air in a box furnace to obtain gradient NMC 622 with a nickel rich core NMC 811 core having a formula of LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂, a first shell of NMC 622 having a formula of LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂ representing the bulk of the volume, and an outer NMC 111 shell having the form LiNi_(0.333)Mn_(0.333)Co_(0.333)O₂. The invention thereby allows the surface characteristics to be different from the bulk. The XRD pattern for the step-wise NMC is provided in FIG. 49 and the SEM is provided in FIG. 50. The discharge capacity as a function of cycles is provided in FIG. 51. A comparative illustration of discharge capacity for NMC 622 (Example 15), NMC 811 (Example 16), NMC 811 fired twice (Example 16), NCA (Example 17) and NMC gradient (Example 18) is provided in FIG. 52 and normalized in FIG. 53.

The invention has been described with reference to the preferred embodiments without limit thereto. One of skill in the art would realize additional embodiments and improvements which are not specifically set forth herein but which are within the scope of the invention as more specifically set forth in the claims appended hereto. 

1-56. (canceled)
 57. A lithium metal oxide cathode comprising: a core comprising Ni and Mn in a first molar ratio; and at least one shell around said core comprising Ni and Mn in a second molar ratio wherein said second molar ratio is different from said first molar ratio wherein said core has a higher ratio of Ni to Mn than said shell.
 58. (canceled)
 59. The lithium metal oxide cathode of claim 55 wherein at least one of said core or said shell has a composition defined by the Formula I: LiNi_(x)Mn_(y)Co_(z)E_(e)O₄   Formula I wherein E is a dopant; x+y+z+e=2; and 0≤e≤0.2
 60. The lithium metal oxide cathode of claim 59 wherein said Formula I is in a spinel crystalline form.
 61. The lithium metal oxide cathode of claim 56 wherein neither x nor y are zero.
 62. The lithium metal oxide cathode of claim 61 wherein said lithium ion cathode material is LiNi_(0.5)Mn_(1.5)O₄.
 63. The lithium metal oxide cathode of claim 59 wherein said cathode material is defined by the formula LiNi_(x)Mn_(y)O₄ wherein 0.5≤x≤0.6 and 1.4≤y≤1.5. More preferably
 64. The lithium metal oxide cathode of claim 63 wherein said 0.5≤x≤0.55 and 1.45≤y≤1.5.
 65. The lithium metal oxide cathode of claim 59 wherein said cathode material has a molar ratio of Mn to Ni of no more than
 3. 66. The lithium metal oxide cathode of claim 65 wherein said cathode material has a molar ratio of Mn to Ni of at least 2.33 to less than
 3. 67. The lithium metal oxide cathode of claim 66 wherein said cathode material has a molar ratio of Mn to Ni of at least 2.64 to less than
 3. 68. The lithium metal oxide cathode of claim 59 wherein said dopant is selected from the group consisting of Al, Gd, Ti, Zr, Mg, Ca, Sr, Ba, Mg, Cr Fe, Cu, Zn, V, Bi, Nb and B.
 69. The lithium metal oxide cathode of claim 59 wherein said dopant is selected from the group consisting of Al and Gd.
 70. The lithium metal oxide cathode of claim 57 wherein said cathode material is defined by the Formula II: LiNi_(a)Mn_(b)X_(c)G_(d)O₂   Formula II wherein G is a dopant; X is Co or Al; wherein a+b+c+d=1; and 0≤d≤0.1.
 71. The lithium metal oxide cathode of claim 70 wherein 0.5≤a≤0.9.
 72. The lithium metal oxide cathode of claim 71 wherein 0.58≤a≤0.62 or 0.78≤a≤0.82.
 73. The lithium metal oxide cathode of claim 70 wherein a=b=c.
 74. A battery comprising the lithium metal oxide of claim
 57. 